WINDSOR LOCKS, Conn. (DC News Now) — A Dulles-bound United Airlines flight had to make an emergency landing on Tuesday, April 18 after a cockpit window opened up while the plane was airborne.

The flight, United Airlines 1274, was scheduled to depart Bradley International Airport (BDL) in Windsor Locks, Conn. at around 6:30 a.m. and arrive at Dulles International Airport (IAD) about an hour and a half later.

Shortly after takeoff, though, something unusual happened.

“We’ve had a window pop open after takeoff,” one of the pilots told air traffic control (ATC). “We don’t have any other issues other than that.”

According to data from FlightRadar24, the flight, operated on a Boeing 737, reached ground speeds of approximately 216 knots (roughly 249 miles per hour) as it looped around the airport. The highest altitude recorded was 4,275 feet. (That’s about the height of the Empire State Building, times three.)

“We’re going to have to come back for a landing,” the flight crew said.

ATC asked the pilots, “United 1274 are you declaring an emergency?”

“Yes, we’re declaring an emergency,” they responded.

In a statement to DC News Now, a spokesperson for United Airlines confirmed the incident.

On Tuesday, April 18, a flight departing Bradley International Airport returned to the airport to address an unlatched cockpit window. The flight landed safely, and we re-accommodated our customers on another aircraft.

Pat Mullane, United Airlines

The Federal Aviation Administration (FAA) said it is investigating. The National Transportation Safety Board (NTSB) confirmed the agency is not reviewing the emergency landing.